Sources: (a) Burke's Extinct & Dormant Baronetcies (b) Burke's Commoners (which states that she was "one of the representatives of the noble family of Umfreville, Earls of Angus (c) Burke's Landed Gentry (d) Pedigree of Blackett, of Wallington.
"coheir, wed Nicholas Blacket of Woodcroft, co. Durham" (Surtees' Durham vol. 2, p.327).
She was included in the Blackett tree accompanying the herald's visitations in 1575, 1615 & 1666, but not in the tree of Tempest of Stella, suggesting she may have been an illegitimate daughter of Rowland.